The present invention relates to gas generating systems and, more particularly, to a pyrotechnic gas generating system containing stored gas for inflating an inflatable vehicle occupant restraint device, such as an air bag.
It is known to use gas generating systems incorporating a stored gas (or “hybrid”) inflator to inflate an inflatable vehicle occupant restraint, such as an air bag, to restrain and protect a vehicle occupant in the event of a collision. One issue with gas generating systems for inflating airbags is the provision of sufficient gas to keep the bag inflated over an extended period of time. In some existing gas generator designs, after a relatively rapid initial generation of gases and inflation of the airbag to a desired volume and pressure, gases may leak or vent from the airbag, thus maintaining sufficient bag inflation for only a relatively short time period. However, some applications require that the airbag be maintained in a sufficiently inflated state for a relatively longer time period.
In addition, it is desirable to generate and distribute the inflation gases as efficiently as possible. However, in some designs, the relatively low temperatures at which the inflation gas is stored and deployed limit expansion of the stored gas, thereby reducing the efficiency of the gas generating system.
In addition, in some gas generating systems utilizing combustion of a gas generant as well as a release of stored gas, to provide inflation gases to an inflatable vehicle occupant restraint device, the gas generant and the stored gas are typically not in fluid communication prior to ignition of the gas generant. Thus, the gas generant is not exposed to the high pressures produced by the stored inflation gas. The relatively low pressure at which the gas generant is stored limits the selection of gas generants to compounds that burn efficiently at relatively low pressures. This precludes the use of alternative (possibly less expensive) gas generants that would burn efficiently at higher pressures.